The RDA for iron is higher in premenopausal women than for men or postmenopausal women because of the blood loss during menstruation.

Correct Answer: A

Rationale: Both the statement and the reason are correct and related. The Institute of Medicine (IOM) recommends 18 mg of iron per day for women 19 to 50 years old, 8 mg/day for women 51 years old and older, and men 19 years old and older. During menstruation, women lose blood containing iron, leading to a higher iron requirement in premenopausal women compared to men or postmenopausal women. This increased demand aims to replenish the iron lost during this physiological process. Therefore, the statement and reason are directly linked, explaining why the RDA for iron is higher in premenopausal women than in men or postmenopausal women. Choices B, C, and D are incorrect as they do not accurately assess the relationship between the statement and the reason provided in the question.

Correct Answer: C

Rationale: Vitamin A can be stored in the liver to meet basic needs for at least 1 year. This storage capacity allows the body to have a reserve of Vitamin A to sustain its needs over an extended period. Choices A, B, and D are incorrect because they underestimate the storage capacity of Vitamin A in the liver, which can last longer than these durations.

Correct Answer: B

Rationale: Both statements are false. Studies suggest that leukoplakia, a white plaque that forms on oral mucous membranes, can be resolved by vitamin A, retinoids, and beta-carotene. Despite the potential to resolve leukoplakia, relapse is common. Also pertinent, evidence does not indicate that any of these nutrients prevent malignant transformation. The extract provided clarifies that leukoplakia is a white plaque, not an erythematous lesion, and that vitamin A, retinoids, and beta-carotene can help resolve it.

Correct Answer: A

Rationale: Both the statement and the reason are correct and related. Inadequate intake of vitamin A in lower socioeconomic groups is due to a lack of resources to purchase and consume vegetables and fruits. This is supported by the fact that the average intake in the United States meets the Recommended Dietary Allowance (RDA) for vitamin A intake, except in lower socioeconomic groups. These individuals often lack the financial means to buy, prepare, and eat a variety of fruits and vegetables, leading to deficiencies. It's important to note that because vitamin A can be stored in the liver, most adults have sufficient quantities to maintain health. Choices B, C, and D are incorrect because the statement and reason are both accurate and logically connected, as the lack of resources directly impacts the ability to obtain necessary sources of vitamin A.

Correct Answer: A

Rationale: Both statements are true. The effect of vitamin A on the growth of soft tissues and bones naturally extends to the teeth and surrounding structures. Enamel hypoplasia, involving defective enamel matrix and incomplete calcification of enamel and dentin, can be due to vitamin A deficiency. The effect of this vitamin upon surrounding bone directly affects spacing patterns of the teeth within the bone and dentition. Choice A is correct because both statements accurately describe the influence of vitamin A on tooth development. Choices B, C, and D are incorrect as they do not reflect the accuracy of the statements provided.